<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <title>遮罩</title>
    <link rel="stylesheet" href="./023.css" type="text/css" />
  </head>
  <body>
    <!--
      如果给box-shadow的扩张半径设定足够大的值，可以用它来遮住背景，而无需额外的div元素
     -->
    <input type="checkbox" id="burger-toggle" />
    <label for="burger-toggle" class="burger-menu">
      <div class="line"></div>
      <div class="line"></div>
      <div class="line"></div>
    </label>
    <div class="overlay"></div>
  </body>
</html>
